Pacemakers are devices that are surgically implanted in the chests of patients to maintain the heart beat at a regular rate. Pacemaker leads are the elongated wires that connect the pacemaker to the heart. The leads are ordinarily comprised of an insulated wire coil terminating with an electrode and are typically passed through the venous system before entering the heart via the superior vena cava. The pacemaker lead electrodes are anchored to the wall of the heart chamber, such as the right ventricle or right atrium, and deliver pacemaker pulse generator charges to the heart muscle and conduct cardiac signals back to the sensing circuit of the pulse generator. Although endocardial pacemaker lead implantation is considered to be a relatively routine procedure, pacemaker lead explantation is still a rather complicated, time-consuming procedure and is associated with significant risk.
The difficulty and risks associated with endocardial pacemaker lead explantation are due to the formation of fibrocollagenous scar tissue adhesions that encase the lead coil to the walls of the veins to the heart and encapsulate the lead electrode in the heart chamber. The longer the pacemaker leads reside within the vasculature and heart chamber, the greater the risks and difficulty of explantation.
Because of the significant risk, pacing leads are typically only removed when life-threatening conditions exist, or to prevent a potentially life-threatening situation from occurring. Mandatory conditions for pacing lead removal include the presence of septicemia (proliferation of infectious agents, such as bacteria and their toxins, in the blood) or endocarditis (inflammation of the inner lining of the heart due to infection).
Pacemaker leads can also fail, necessitating replacement, or no longer be required. Reasons for failure include lead fracture, insulation deterioration, or an increase in electrode resistance, thereby impeding the passage of the signals between the pacemaker and the heart. Migration of severed endocardial leads, causing mechanically induced ventricular arrhythmia, and protrusion of lead coil wires from the insulation are also considered mandatory conditions for lead removal. However, in many instances the risk of removing failed or unused pacemaker leads, using current methods, is greater than the risk of leaving them in place. In these situations, they are usually capped off and left anchored to the wall of the heart chamber.
Unfortunately, there are substantial risks associated with leaving failed and unused leads in place. The risks of leaving these leads in place include an increased likelihood of infection or blood clot formation around the old and entangled pacing leads. Other complications associated with leaving failed and unused leads in place are that the leads can restrict the operation of the heart valves and hinder the implantation of new leads in the heart. Thus, it is preferable to remove unused and failed leads whenever possible.
There are currently three principal techniques for endocardial pacemaker lead explantation. These techniques include traction, the combined use of traction and countertraction, and cardiac surgery.
With traction, the pacemaker lead is pulled directly or with the aid of a snare or catheter. U.S. Pat. No. 4,574,800, of Peers-Traverton, describes a device for applying traction to a pacing lead. The drawbacks of this technique include the fact that the procedure involves significant risk and is oftentimes unsuccessful. Associated complications include arrhythmias (irregular heart beat), low blood pressure, the inward pulling of the heart wall towards the heart valve, or even rupture of the heart wall. In addition, the pulling force may cause the pacemaker lead to be distorted or broken, impeding the ability to use other transvenous techniques. If the lead is severed, surgical removal is required.
The use of traction combined with countertraction has been shown to be less hazardous than traction alone but the technique is complicated and procedure success is highly dependent on the skill and experience of the physician. This method is also associated with relatively high complication rates. The technique most often practiced involves the use of a locking stylet, which is a wire that is advanced through the lumen of the pacing lead coil until it reaches the distal portion of the lead. The distal tip of the wire is configured with a fine wire coil that is wound clockwise so that when the stylet wire is rotated counterclockwise, the distal tip locks into the lead coil. The proximal end of the stylet can be shaped into a loop to act as a handle when applying traction. The purpose of the locking stylet is to provide stiffness and tensile strength to the pacing lead coil and deliver traction force directly to the distal tip of the lead. Once the locking stylet is in place, countertraction is applied by advancing one, or more commonly two, stainless steel, PTFE, or polypropylene sheaths over the stylet/pacing lead coil. When two sheaths are used, they are advanced in a telescoping fashion with one inside the other. The telescoping sheaths are passed over the pacemaker lead and when scar tissue is encountered, the sheaths are manually pushed, generally with substantial force, through the scar tissue adhesions by dilating, tearing and sliding over the tissue. Once the distal tips of the telescoping sheaths reach an area close to the electrode in the heart chamber, the electrode is freed from the fibrous cap in the chamber by pulling on the locking stylet.
The traction/countertraction method is a complex procedure and is highly dependent on physician skill and experience. Two critical aspects are 1) how hard to pull on the locking stylet, and 2) how hard to push the telescoping sheaths. Applying too much pulling or pushing force increases the risk of tearing the vein or heart chamber, or damaging the pacing lead wire. If the lead is severed, surgical removal is required.
Much of the procedure complexity is attributed to the complexity of the devices currently used to apply traction and countertraction. For example, U.S. Pat. Nos. 4,471,777, 4,582,056 and 4,576,162, all of McCorkle, describe a composite assembly of three catheters and method for endovascular lead extraction. The three catheter assembly includes a tool for applying tensile force to the electrode lead (the grasping catheter) and two catheters, one positioned over the other, with outward facing sharp serrations for separating scar tissue from the pacing lead and electrode. U.S. Pat. Nos. 4,943,289, 4,988,347, 5,011,482, 5,013,310, and 5,207,683, all of Goode et al., describe a stylet wire that attaches to the pacemaker electrode and separator tube, comprised of a hollow tube made of semi-rigid material, for separating the pacemaker lead from the vessel wall.
The third commonly practiced pacemaker lead extraction method is surgical removal. Surgery is also associated with significant risk and high cost. Additionally, not all patients, such as ill and elderly patients, are surgical candidates.
Another method, although still being investigated and therefore not widely practiced, involves the application of laser energy to separate pacemaker leads from scar adhesions. Theoretically, the cutting action of the laser reduces the amount of mechanical force required to separate the pacemaker lead from the vascular structure, thereby reducing the potential for rupturing the vessel or heart chamber wall. The main drawback of this method, however, is that it requires the use of highly complex and expensive laser technology.
Many surgical instruments exist with various cutting blade designs and mechanisms for separating objects from biological tissues. However, none of these instrument designs are appropriate for the removal of an elongated object, such as a pacemaker lead. For example, a variety of rigid mechanical cutting instruments are known for various other surgical applications, such as U.S. Pat. Nos. 4,461,305 of Cibley, 5,047,008 of de Juan et al., 4,306,570 of Matthews, 5,324,300 of Elias et al., 5,112,299 of Pascaloff, 5,275,609 and 5,290,303 of Pingleton et al. Since these devices are not flexible, their application is limited to straight passageways. Different flexible cutting instruments are described by U.S. Pat. Nos. 4,729,763 of Henrie, 4,754,755 of Husted, and 5,152,744 of Krause et al. U.S. Pat. No. 4,729,763 of Henrie describes a catheter comprised preferably of steel wire with a blade tip that is rotated using a motor drive, and U.S. Pat. No. 5,152,744 of Krause et al. describes a flexible instrument with rigid proximal and distal ends. The flexibility of this device is achieved by cutting grooves or holes into the tube. U.S. Pat. No. 4,646,738, of Trott, describes a rotatable surgical tool containing a tubular flexible coupler, comprised of a plurality of coaxial spirally wound layers for transmitting rotational movement. None of these mechanical cutting instruments, whether flexible or rigid, utilize a metal bellows for flexibility, trackability, blade extension, or torque transfer to the distal blade. Additionally, none of the instruments involve a cutting mechanism comprised of concurrent blade extension and rotation.
To overcome the problems encountered with removal of pacemaker leads from the heart, it is necessary to use an instrument that provides precise, controlled cutting. The instrument should be capable of precise placement of the blade before cutting takes place. The extension and rotation of the blade should be controlled and limited. Additionally, the blade's resting position should be within a secure housing, to eliminate the potential for accidental cutting or shearing. A desired instrument would alternately function as a dilating device when the cutting edge is in a resting position.
The present invention is intended to overcome one or more of the problems of the prior art devices discussed previously, and meet the requirements of a device suitable for extraction of pacemaker leads or other objects that may become embedded in biological tissue.